Novel low pressure back-fill and process therefore

ABSTRACT

There is provided a novel form of back-fill for vertical retaining walls and a method of producing the same. The novel form of back-fill comprises a layer of moderately rigid, synthetic, polymeric foam located between the interface of a retaining wall and the soil which it is intended to retain. This plastic layer replaces sand or soil customarily used for this purpose. The novel back-fill makes possible the use of retaining walls of considerably lower strength than have been needed heretofore. The novel back-fill also permits easier drainage of the space behind the retaining wall.

nite tates Patet 1 [111 3,747,353 Monahan July 24, 1973 [54] NOVEL LOW PRESSURE BACK-FILL AND 2,115,009 4/1938 Doncaster 61/39 PROCESS THEREFORE Inventor: Edward J. Monahnn, 85 Newark Ave., Bloomfield, NJ. 07102 Filed: Dec. 13, 1971 Appl. No.: 207,400

Related U.S. Application-Data Continuation-in-part of Ser. No. 10,843, Feb. 12, 1970, Pat. No. 3,626,702.

U.S. Cl 61/39, 61/49, 61/50, 52/169 Int. Cl. E02d 29/00 Field of Search 61/39, 49, 50; 52/169 References Cited UNITED STATES PATENTS Monahan 61/50 Primary Examiner-David .l. Williamowsky Assistant Examiner-Alexander Grosz Attorney-Thomas Cifelli, Jr. et al.

[57] ABSTRACT There is provided a novel form of back-fill for vertical retaining walls and a method of producing the same.

The novel form of back-fill comprises a layer of moderately rigid, synthetic, polymeric foam located between the interface of a retaining wall and the soil which it is intended to retain. This plastic layer replaces sand or soil customarily used for this purpose. The novel back-fill makes possible the use of retaining walls of considerably lower strength than have been needed heretofore. The novel back-fill also permits easier drainage of the space behind the retaining wall.

11 Claims, 3 Drawing Figures Pmmwm FIG FIG. 3

NOVEL LOW PRESSURE BACK-FILL AND PROCESS THEREFORE RELATED APPLICATIONS This application is a continuation-in-part of Applicants co-pending application, Ser. No. 10,843, filed Feb. I2, 1970, US. Pat. No. 3,626,702, issued Dec. 14, 1971.

FIELD OF THE INVENTION Novel back-fill procedures.

DESCRIPTION OF THE PRIOR ART The use of retaining walls in the construction of buildings, highway projects, embankments, and the like, is well known in the civil engineering art. These walls generally fall into two categories. In one category the wall is part of a structure which is inserted into a volume of soil, for example, the outer wall of a cellar. In this case the function of the wall is not only to bear the vertical pressure of the building erected upon it but also to resist the lateral pressure of the soil surrounding the cellar excavation.

The other type of retaining wall is used, for example, in retaining the soil utilized to build an embankment, for example, for the purposes of a road which is required to run substantially at a given level. If the retaining wall is not utilized the volume of soil required to build a stable embankment would be considerably greater. Hence, the retaining wall replaces a substantial volume of soil.

In yet another modification of the second type of retaining wall, a downward slope is required to be built up to a horizontal level and a retaining wall placed between the lower'portion of the slope and the newly desired horizontal and the volume back-filled with soil in order to provide the new level.

In all of the cases mentioned above, substantial lateral pressure is brought to bear upon the vertical face of the wall adjoining the soil by the weight of the soil itself. In some cases, in particular, in the third case mentioned above, this pressure has been somewhat modified byusing a back-fill material such as sand which is lighter than soil. However, the back-fill pressure of sand is still considerable and the expense of the material is substantial. Furthermore, the use of soil as back-fill possess problems of drainage which, although they have been well recognized and well solved in the art, still require the outlay of substantial capital expense in order to prevent the build-up of water at the soil wall interface.

It was therefore deemed desirable to seek an alternate mode of back-till to replace soil and sand and the like which would reduce the lateral pressure on the wall and, if possible, simplify the problems of drainage.

SUMMARY OF THE INVENTION It has been discovered that the stabilizing influence provided by conventional back-fillmaterials, such as sand, gravel and the like can be provided by synthetic polymeric foams, suitably rigid synthetic polymeric foams, which possess sufficient compressive strength to support substantial structures while at the same time having a density far less than that of these conventional materials. The pressure credit which is obtained by using such foams in place of conventional back-fill materials, may be translated into a reduction in lateral pressure upon such certain types of vertical retaining walls, thus making possible substantial savings in the construction of such walls since they would no longer be required to resist the lateral pressure heretofore placed upon them.

It should be noted that while the novel system of the present invention possess great advantages in the cases mentioned above which fall into the category known in the art as the active case it cannot be utilized satisfactorily in what is known in the art as the passive case.

It will be recognized by those skilled in the art that where a retaining wall is installed in any item of construction it comprises not merely a wall having a vertical component but also of a footing in the nature of a foundation having a substantially horizontal component. The wall is anchored to this substantially horizontal footing. In any construction utilizing a retaining wall, the soil pressures behind the retaining wall will tend to cause the wall to rotate either away from the soil bank or towards it. The former is known as the active case and the latter is known as the passive case."

It should be understood that the back-fill of the present invention finds primary use in the active case since it will be seen that in the passive case there would be a tendency for the lightfoam insert to pop out of the volume in which it is placed. This of course would not occur in the active case.

In the active case, as illustrated by FIG. 2 Section (A) is presented to act with thewall and thus is regarded as part of wall 40 for purposes of pressure credit calculations.

As stated hereinabove we are only concerned with the active case, i.e., where the'soil friction angle d: (the angle above which free standing soil would slip) is less than the angle subtended by the soil slope to the horizontal. As will be seen hereinbelow the actual angle of slope O is not relevant to the calculations of pressure relief.

Thus in the active case the actual pressure on the wall 40 is expressed as Pz where where Kap is the coefficient of plastic pressure at rest 7 p is the density of the plastic and H is the maximu depth of the wall w and H should be inconsistant units, i.e., lb/cu ft. ft or Kg/m and m. Kap can be assumed to be unity.

Similarly the pressure due to the wedge of soil removed from behind the wall and replaced by the plastic 18 Ps where Ps Ks y s 1-1/2 where Ks is the coefficient of soil pressure at rest and is expressed as Ks (l sin )/(l sin d1) 'ys is the density of the soil and H is as above. Similarly 7s H are expressed in consistent units.

EXAMPLES OF PRESSURE CREDIT The following values are typical values found in practice.

7s 120 lb/cu. ft. 7 p 4 lb/cu. ft. :1: (for typical granular soil) 30 Then Ps P: H/2 (120 X (lO.5/l+0.5) 4) Thus, the pressure credit is 18 lbs. sq. ft. per foot of depth.

Since the pressure caused by the soil per se is 20 lb./sq. ft. per foot of depth, this represents a pressure saving of 90 percent.

It has been discovered that the stabilizing influence provided by conventional backfill materials such as sand, gravel and the like can be provided by synthetic polymeric foams, suitably rigid synthetic polymeric foams, which possess sufficient compressive strength to support substantial structures while at the same time having a density far less than that of these conventional materials. The weight credit which is thus obtained by using such foams in place of conventional backfill materials may then be used in constructing structures of greater weight, presumably higher structures, on a given area of land than was heretofore possible.

Many different foams are known in the polymer art which can be used for the provision of such subfoundations. There may be mentioned polyurethane foams, polystyrene foams, epoxy foams, phenolic foams, urea formaldehyde foams and syntactic polyvinyl chloride foams, although the scope of the present invention is in no way considered as limited to these named foams. Urethane foams are the foams of choice since these foams are comparatively inexpensive, can be formulated into compositions of very substantial compressive strength using formulations which are well known in the art and these foams may be readily prepared by a variety of methods.

The present invention is readily distinguished from the Jorczak method U.S. Pat. No. 3,367,892 in that Jorczak seeks to stabilize an unstable soil by providing structural links between the soil particles, while the present method contemplates the total removal of a precalculated amount of soil and its replacement by a polymer foam to provide a weight credit.

The foams, in particular the urethane foams, may either be manufactured in situ to fit the specific dimensions of the foundations, or the subfoundation may be constructed from slabs of prefabricated foam having the necessary mechanical qualities which are shipped to the site of the building ready made. Both modes are to be considered to be within the scope of the present invention.

Since the art of foam production is extremely voluminous, no useful purpose would be served by detailing all the modes for the production of such foams. Reference is made, however, to T. H. Ferrigno, Rigid Plastic Foams, 2nd Edition, Reinholdt Publishing Corporation, New York 1967, J. H. Saunders and C. K. Frisch, Polyurethane, Part 2, Chemistry and Technology, Interscience Publishers, New York, 1964; S. M. Kujawa, High Density Urethane Foam Prepared by the One-Shot Technique, Journal of Cellular Plastics, Vol. 1, page 400, 1965, and Cear et al, SPE Technical Papers, Reports of the Technical Conference (Buffalo), Plastic Foams, paper 76 (Oct. 5, 1961).

DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional elevational view of a retaining wall showing replacement of soil by plastic.

FIG. 2 is a schematic view of FIG. 1 indicating the angle of slope of the soil.

FIG. 3 is a modification of the view of FIG. 1 showing a roadbed on the plastic layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the process of the present invention, the area behind retaining wall 40 which a building, roadbed, runway, pipeline, or the like is to be constructed, is excavated to provide a predetermined amount of pressure release from the sub-soil behind the retaining wall structure will rest. In FIG. 1, the sub-soil 11 is excavated to give excavation 10.

A substantial portion of the excavation 10 is filled with a rigid polymeric foam 12. While it is permissible to use any foam with sufficient compressive strength and resistance to water, it is especially preferred to use a rigid urethane foam which may be either cast at the site of the excavation or shipped in, in the form of precast slabs.

Urethane foams are preferred principally for reasons of cost but also since their properties may be readily varied to suit the desired conditions by means and formulations well known in the art. The urethane foams utilized in the practice of the present invention are designated as rigid urethane foams. While it is understood that the relationship between the compressive strength of a foam and its density may be varied in accordance with the formulation selected, it has been found that the most suitable range of foams are those having a compressive strength of psi and a density of 4 lb. per cubic foot through those having a compressive strength of 1000 psi and a density of 20 lb. per cubic foot. This range should be in no way considered as limiting upon the invention, since foams having a compressive strength of at least 30 lb. per square inch and a density of 3 lb. per cubic foot may also be utilized in the invention, and foams having even lower compressive strengths and densities may be found useful.

The selection of a foam having a particular density must be made after taking into consideration all the circumstances of the individual case. Thus high density foams are clearly more expensive than the lower density foams due to increased cost of materials. This increase in cost must be measured against increase in compressive strength in what is substantially an exponential relationship. Furthermore, particularly when on-site production of the foam is contemplated, it should be recognized that the production of high density foams of uniform properties becomes more difficult as the density increases. This factor is due to the decreasing heat conductivity of the foams with increase in density since considerable amounts of heat are generated during the actual polymerization step and such considerations must be taken into account. However, methods for assuring satisfactory distribution of compressive strength are well known in the art.

The preferred technique for preparing the high density polyurethane foams used as backfill in the present invention is the so-called one shot technique. In this technique two carefully metered streams are brought together, one stream containing a polyhydroxy compound such as Heterofoam (produced by Hooker Chemical Corporation) and a prepolymer or polyisocyanate stream. Optionally, the polyhydroxy stream may contain a catalyst, or when water is to be the blowing agent, the water component. The isocyanate stream contains the halocarbon blowing agent. Since the halocarbon blowing agent, suitably a polyhalohydrocarbon such as a polyfluorohydrocarbon is not reactive either with the isocyanate or the polyol, it may be also carried in the polyol stream. However, water being reactive with isocyanate cannot be carried in the isocyanate stream.

Thus it will be seen that both halocarbon and water may be utilized as the blowing agent.

Generally speaking it has been found that where foams having a density in excess of 6 lb. per cubic foot are to be produced, it is not necessary to employ a catalyst since the use of such a catalyst would cause too rapid a rise in the internal temperature of the foam during the polymerization step.

If desired a cell controller of the type known in the art may be utilized to control excessive size of the bubbles arising from the blowing agent system. It has been found, however, that where the foams projected are in the 10 to lb. per cubic foot range such cell controllers are not necessary.

In the production of subfoundations in accordance with the present invention, conventional polyurethane components such as those discussed above are mixed in conventional one-shot machinery and injected into the excavation to foam layer 12 as shown in FIG. 1. In dealing with high density urethane foams care must be taken that each layer of foam deposited be not excessively thick in order to avoid scorching and cracking of the foam in the process of formation. While not to be taken as limiting conditions, nevertheless it is advisable where foams of 6 lb. per cubic foot density are to be utilized each layer be not in excess of 14 inches in thickness or if a density as high as 24 lb. per cubic foot is required, the layer thickness should not be in excess of 5 inches. These depths of course can be well controlled by means familiar to those skilled in the art. Thus where the subfoundations-are precast, the slabs shouldnot exceed those dimensions. Similarly where in situ casting is employed, the foundations'are cast in layers corresponding to those thicknesses. Conventional engineering techniques may be employed to prevent the sliding of layers over each other. In the construction of roads or runways for aircraft behind the retaining wall an excavation 30 is similarly filled with the layer of foam 32 which is then covered with the substantially rigid layer 36 which may comprise concrete, low mesh asphalt, orthe like and a surface layer 34 which may be concrete or high mesh asphalts. If desired, intermediate layer 36 may be omitted.

As examples of the formulation and production conditions for formation of certain foams within the scope of the present invention, the following may be mentioned. However, these examples are given for purposes of exemplification only and not for the purposes of limitation.

EXAMPLE I CONDITIONS FOR PRODUCING 20 PCF FOAM 6 INCHES BUN Form ulation:

Heterofoam Polyol 100 pts. (Polyol Steam) Polyphenyl Isocyanate 84 pts. Halocarbon Blowing Agent 3 pts. (Isocyanate Steam) Cell Controller 0.5

Machine Conditions:

Polyol/Isocyanate Steam 1 l4.3/l00 Dispense Rate, PPM 28.6 Mixer Speed, RPM 5000 plus Polvol Temperature, F 1 l2 Isocyanate Steam Temp., F N, Pad on Reservoirs, Psig. 15

I. Registered trademark, Hooker Chemical Corp.

EXAMPLE 2 CONDITIONS FOR PRODUCING 4 PCF FOAM 12 INCHES BUN Formulation:

Heterofoam Polyol pts. (Polyol Steam) Polyphenyl isocyanate 84 pts.

Halocarbon Blowing Agent 12 pts. (lsocyanate Steam) Cell Controller 1 pt.

Machine conditions:

Polyol/Isocyanate Steam l03.l/l00 Dispense Rate, PPM 28.6

Mixer Speed, RPM 5000 plus Polyol Temperature, F

Isocyanate Temp., F 70 EXAMPLE 3 CONDITIONS FOR HIGH RISE 8 N Pad on Reservoirs, Psig.

No Pad on Reservoirs, Psig. Substrate Temp., "F I50 What we claim is: l. A back-fill for a retaining wall relieving the latera pressure on the wall, which comprises a Section of rigid foam plastic placed adjacent to said wall, said foam layer replacing soil orginally adjoining said wall wherein:

Pz is the lateral pressure on the wall at the base thereof. Ka is the coefficient of earth pressure at rest Kap is the coefficient of plastic pressure at rest 'y s is the density of the soil y p is the density of the plastic (1) is the soil friction angle and 0 is angle between the excavated soil and the horizontal plane of the plastic foam placed thereon, and 0 100 K,= (l sin )/(l sin (11),

c is the compressibility of the foam then:

2. A backfill for a retaining wall according to claim I additionally comprising a rigid platform located on top of the foam layer.

3. A back-fill according to claim 2 wherein the foam comprises a foam selected from one or more members of the group consisting of polyurethane, polystyrene, phenolic epoxy, urea formaldehyde, and syntactic polyvinyl chloride foams.

4. A backfill according to claim 1 wherein said foam has a density of between 3 and lb. per cubic foor and a compressive strength of between 30 and 1000 lb. per square inch.

5. A backfill according to claim 1 wherein the foam is polyurethane foam having a density of at least 3 lb. per cubic foot and a compressive strength of at least 30 lb. per square inch.

6. A processing for providing a backfill for a retaining wall according to claim 1 which comprises the steps of a. excavating the soil behind said wall b. partially filling said excavation with a rigid polymeric foam.

7. A process according to claim 6 wherein the polymeric foam is produced in the site of the excavation.

8. A process according to claim 6 wherein the foam layer is produced by casting thin layers of foam on top of each other.

9. A process according to claim 6 wherein the polymeric foam is precast and subsequently installed in the foundation in slab form.

10. A process according to claim 6 wherein the polymeric foam is foam selected from a group consisting of polyurethane, polystyrene, epoxy, phenolic urea formaldehyde, and syntatic polyvinyl chloride foams.

11. A process according to claim 6 wherein the foam is polyurethane foam having a density of at least 3 lb. per cubic foot and a compressive strength of at least 30 lb. per square inch. 

2. A backfill for a retaining wall according to claim 1 additionally comprising a rigid platform located on top of the foam layer.
 3. A back-fill according to claim 2 wherein the foam comprises a foam selected from one or more members of the group consisting of polyurethane, polystyrene, phenolic epoxy, urea formaldehyde, and syntactic polyvinyl chloride foams.
 4. A backfill according to claim 1 wherein said foam has a density of between 3 and 20 lb. per cubic foor and a compressive strength of between 30 and 1000 lb. per square inch.
 5. A backfill according to claim 1 wherein the foam is polyurethane foam having a density of at least 3 lb. per cubic foot and a compressive strength of at least 30 lb. per square inch.
 6. A processing for providing a backfill for a retaining wall according to claim 1 which comprises the steps of a. excavating the soil behind said wall b. partially filling said excavation with a rigid polymeric foam.
 7. A process according to claim 6 wherein the polymeric foam is produced in the site of the excavation.
 8. A process according to claim 6 wherein the foam layer is produced by casting thin layers of foam on top of each other.
 9. A process according to claim 6 wherein the polymeric foam is precast and subsequently installed in the foundation in slab form.
 10. A process according to claim 6 wherein the polymeric foam is foam selected from a group consisting of polyurethane, polystyrene, epoxy, phenolic urea formaldehyde, and syntatic polyvinyl chloride foams.
 11. A process according to claim 6 wherein the foam is polyurethane foam having a density of at least 3 lb. per cubic foot and a compressive strength of at least 30 lb. per square inch. 